Geological Society of America 3300 Penrose Place P.O. Box 9140 Boulder, CO 80301 (303) 357-1000 • fax 303-357-1073 www.geosociety.org Chapter 12: “Middle to late Cenozoic geology, hydrography, and fish evolution in the American Southwest” (Spencer et al.), in Reheis, M.C., Hershler, R., and Miller, D.M., eds., Late Cenozoic Drainage History of the Southwestern Great Basin and Lower Colorado River Region: Geologic and Biotic Perspectives: Geological Society of America Special Paper 439. This PDF file is subject to the following conditions and restrictions: Copyright © 2008, The Geological Society of America, Inc. (GSA). All rights reserved. Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in other subsequent works and to make unlimited copies for noncommercial use in classrooms to further education and science. For any other use, contact Copyright Permissions, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA, fax 303-357-1073, [email protected]. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. This file may not be posted on the Internet. The Geological Society of America Special Paper 439 2008 Middle to late Cenozoic geology, hydrography, and fish evolution in the American Southwest Jon E. Spencer Arizona Geological Survey, 416 W. Congress St., Suite 100, Tucson, Arizona 85701, USA Gerald R. Smith Museum of Zoology, and Museum of Paleontology, University of Michigan, Ann Arbor, Michigan 48109-1079, USA Thomas E. Dowling School of Life Sciences, P.O. Box 874501, Arizona State University, Tempe, Arizona 85287-4501, USA ABSTRACT An evaluation of the poorly understood Cenozoic hydrologic history of the Ameri- can Southwest using combined geological and biological data yields new insights with implications for tectonic evolution. The Mesozoic Cordilleran orogen next to the conti- nental margin of southwestern North America probably formed the continental divide. Mountain building migrated eastward to cause uplift of the Rocky Mountains during the Late Cretaceous to early Tertiary Laramide orogeny. Closed drainage basins that devel- oped between the two mountain belts trapped lake waters containing fish of Atlantic affinity. Oligocene-Miocene tectonic extension fragmented the western mountain belt and created abundant closed basins that gradually filled with sediments and became con- duits for dispersal of fishes of both Pacific and Atlantic affinity. Abrupt arrival of the modern Colorado River to the Mojave-Sonora Desert region at ca. 5 Ma provided a new conduit for fish dispersal. Great dissimilarities in modern fish fauna, including differ- ences in their mitochondrial deoxyribonucleic acid (DNA), indicate that late Miocene runoff from the Colorado Plateau did not flow down the Platte or Rio Grande, or through the Lake Bonneville Basin. Fossil fishes from the upper Miocene part of the Bidahochi Formation on the Colorado Plateau have characteristics that reflect a habitat of large, swift-moving waters, and they are closely related to fossil fishes associated with the Snake and Sacramento Rivers. This evidence suggests that influx of fishes from the ancestral Snake River involved a major drainage, not merely small headwater transfers. Keywords: Colorado River, drainage evolution, fish evolution, continental divide, Bidahochi Formation. INTRODUCTION by continued tectonic activity (Cowan and Bruhn, 1992; Miller et al., 1992; Christiansen and Yeats, 1992). This long geologic The middle to late Cenozoic evolution of rivers and history can be divided into four major stages, as follows: (1) Late drainages in southwestern North America occurred on a stage that Jurassic and Cretaceous magmatism and faulting created a moun- was set by the previous 100 m.y. of geologic history and modified tain belt adjacent to the southwestern edge of the North American Spencer, J.E., Smith, G.R., and Dowling, T.E., 2008, Middle to late Cenozoic geology, hydrography, and fish evolution in the American Southwest, in Reheis, M.C., Hershler, R., and Miller, D.M., eds., Late Cenozoic Drainage History of the Southwestern Great Basin and Lower Colorado River Region: Geologic and Biotic Per- spectives: Geological Society of America Special Paper 439, p. 279–299, doi: 10.1130/2008.2439(12). For permission to copy, contact [email protected]. ©2008 The Geological Society of America. All rights reserved. 279 280 Spencer et al. continent that became a major drainage divide. The east side of Susquehanna, Ohio, and Mississippi headwaters (C.L. Smith, this mountain belt includes the Cordilleran fold-and-thrust belt, 1985), while cold-water fishes indicate routes of entry through which extends from southernmost Nevada through the Idaho- glacial outflow streams. The principle guiding this source of Wyoming border region and northward to Yukon Territory, and a hydrographic evidence is that fishes readily colonize suitable complex and poorly understood belt of crustal thickening and habitats, usually through habitable waters, after gaining access. magmatism that extends southeastward from southernmost The ranges of freshwater fish species and genera may be Nevada through the Mojave-Sonora Desert region and into north- restricted by variations in salinity, temperature, stream gradient, ern Mexico. (2) Latest Cretaceous to early Tertiary reverse and and current velocity, as well as competition and predation. The thrust faulting and magmatism during the Laramide orogeny nature of past dispersal routes can be inferred from the morpho- formed the Rocky Mountains and created multiple basins, some logical and physiological characteristics of the dispersed species of which trapped lake waters. (3) Oligocene-Miocene crustal or genera. For example, capture of small headwater drainages extension generally reduced elevations and converted much of allows transfer of only small, usually cooler-habitat headwater the mountain belt formed in stage 1 into numerous small ranges species, so the kinds of species found across a drainage divide and intervening basins that now make up the Basin and Range tec- suggest the size and elevation of the aquatic connection. A latent tonic and physiographic province. Voluminous magmatism at this pattern may remain for hundreds of thousands of years or more time also modified landscapes. Drainages within this region were because of subtle ecological barriers and because evolutionary typically closed, and streams ended at playas or lakes. (4) During changes are usually slow and gradual in fishes—evolution of the last 10–15 m.y., Baja California and southwestern California reproductive isolation takes thousands to millions of years in the have been displaced obliquely away from mainland Mexico, groups considered here (Smith et al., 2002). The missing element which has opened up the Gulf of California and provided an out- from evidence of past connections, until recently, has been a mea- let to the sea for nearby drainages in the Basin and Range sure of time. Province. This event also formed the Transverse Ranges in south- Use of deoxyribonucleic acid (DNA) nucleotide sequences as ern California. a chronometer of branching points in fish evolution has provided The geologic record of river courses and evolution is remark- a new tool for discerning the surface hydrologic history of ably poor. Typically, sediment accumulations derived from paleo- drainage basins. Development of DNA sequencing technology rivers cannot be associated with well-defined river catchments and methods for using fossils to calibrate the rate of mutation accu- because of weak specificity of clast types with regard to source mulation allow the evolutionary divergence times between fish area. Furthermore, voluminous river-terminus sediment accumu- groups to be estimated on geological time scales. The segregation lations generally consist of sand and silt, and conglomerate clasts, of freshwater fish faunas by the appearance of geographic barriers if present at all, may represent only the most proximal sediment caused by tributary capture, desiccation, waterfalls, volcanism, or sources or the most resistant rock types. Incised river courses in tectonics, is now subject to age estimates based on mitochondrial intermountain areas typically leave little or no sediment accumu- DNA (mtDNA) nucleotide-sequence chronometers. lation along their upstream course, and paleoriver valleys and Two similar expressions of genetic distances are in common canyons may be obscured by tectonic disruption or erosional use—pair-wise and single lineage rates of molecular substitution destruction, or they may be completely buried by volcanic and (the former is generally 2ϫ the latter) (Swofford et al., 1996). In sedimentary rocks. Tectonic disruption and burial were so severe this method, the numbers of genetic substitutions, reported as per- during Oligocene-Miocene extension and magmatism in the centage of nucleotide differences in homologous DNA sequences Basin and Range Province that almost nothing can be confidently or modeled as maximum likelihood differences in phylogenetic stated about pre–late Cenozoic river courses and evolution from tree-branch